In the field of display technology, a photodiode display panel has become a hot spot of current display research because of its high response speed, high color gamut, high contrast ratio, wide viewing angle, ultra-thin, low power consumption and so on. A light emitting diode display panel includes a bottom emission mode and a top emission mode. In the bottom emission mode of the light emitting diode display panel, a white organic light emitting diode (OLED) is made underneath a thin film transistor TFT array. The fabrication process is relatively simple. However, a metal wiring can block the light emitted by the OLED, resulting in a decrease in the aperture ratio and difficulty in manufacturing high PPI (pixels per inch) products. In the top-emission mode, a white OLED emits light above the active matrix. There is no problem of shielding the light by the metal wiring, and it has the advantage of high aperture ratio, so it is widely used.
The top emission mode has two structures, in which one structure is obtained by combining a substrate having a TFT array and an OLED with a cover plate coated with a color filter layer through a spacer, in which the combination of the array substrate and the color film cover plate requires a certain height in the alignment to avoid the impact of particulate matter on the OLED. If the height of the combination is too low, the combination cannot be performed because the alignment precision of the device cannot meet the requirements. If the height of the combination is too high, the size of the black matrix should be increased to prevent light leakage, and thus the aperture ratio is reduced. Another structure of the top emission mode is to fabricate the color filter layer directly on the OLED, and then encapsulate it with the cover plate, and this structure can effectively improve the aperture ratio.
In the conventional OLED back plate, in the preparation of a planarization layer, a reflective anode layer, and a pixel definition layer, three masking processes needs to be implemented, and the processes is more. If the pixel definition layer is not used, because metal boundaries of the reflective anode are relatively rough, and various layers in the OLED device are very thin, a short circuit may occur at the metal boundaries of the anode during an evaporation process, resulting in dark spots, which may affect the yield of the product.
It should be noted that, information disclosed in the above background portion is provided only for better understanding of the background of the present disclosure, and thus it may contain information that does not form the prior art known by those ordinary skilled in the art.